Several methods are known for the production of an element subject to wear, wherein such element substantially comprises a metal matrix, which confers a high level of rigidity and strength to the element, and a core of ceramic material with a high resistance to abrasion.
A first known method, for example described in EP-A-0.930.948, provides to make an element subject to wear with a size of more than 25 mm by means of casting, or centrifuging, a molten metal material on an insert, or biscuit, made of ceramic material, arranged in a mold. The insert consists of a homogeneous solid solution of 20%-80% in weight of Al2O3 and 80%-20% in weight of ZrO2.
A second known method, for example described in EP-A-0.841.990, provides to cast the molten metal material on a ceramic insert of metal oxide and/or metal carbide, with a perforated or spongy structure, so that, during casting, the molten metal material can penetrate into the apertures and interstices of the insert.
Both these known methods, however, do not allow to obtain elements having mechanical characteristics such as to be employed in any application and field whatsoever, including those with heavy stresses and intense and continuous strain, and which require properties of hardness, toughness and resistance to temperature which cannot be obtained with said methods.
From EP-A-0042130 it is known a method to manufacture ceramic shaped articles by sintering or hot pressing a mixture of dense, non-metallic, mechanically resistant ceramic materials, which contain eutectic constituents consisting of zirconium oxide, hafnium oxide and at least one other high-melting oxide and mixtures thereof. This known method comprises a step wherein a powder is mixed in a hypoeutectic, eutectic, or hypereutectic ratio, is heated to its melting point and, after a rapid cooling, is pulverised and poured into a. Then, the articles are shaped by sintering or pressure-sintering in a pre-heated mould utilizing the resulting powder. Therefore, this known method has the disadvantage to provide for a heating cycle in order to cause the aggregation of the particles of the different ceramic materials which form the mixture.
Purpose of the present invention is to perfect a method versatile enough to obtain elements subject to wear, such as a mechanical member, an abrasion or crushing tool or suchlike, whose characteristics can be pre-determined so as to be able to use them in a wide range of applications. To be more exact the method must allow to obtain elements subject to wear which have a high resistance to wear, optimum toughness and are able to resist considerable stresses, including thermal stresses, and also prolonged strain.
Another purpose is to achieve an element subject to wear wherein the core made of ceramic material does not have to be reinforced internally in order to be positioned stably in the mold, before the molten material is cast, that is, that the core is of the self-supporting type.
Another purpose of the present invention is to achieve a method wherein it is not necessary to pre-heat the mold and the core made of ceramic material before casting the metal material.
Applicant has devised, tested and embodied the present invention to obtain these and other purposes, to achieve other advantages and to overcome the shortcomings of the state of the art.